Apparatus for securing together straps made of thermoplastic material

ABSTRACT

Apparatus for binding together thermoplastic strap portions by rotating a lever which actuates means for interposing the end of a continuous strip of wire screening between the strap portions,. The end is severed from the strip when the press means, also actuated by the lever, forces the strap portions together. When severed, the screening is wedged between two electrodes in the press means and completes an electrical circuit which is activated by the lever contacting a timing device at the end of its stroke. The electrical current heats the screening which fuses the thermoplastic strap portions together.

Jan. 1, 1974 H. W EHR 3,783,079

-' APPARATUS FOR SECURlNG TOGETHER STRAPS MADE OF THERMOPLASTIC MATERIAL Filed Dec. 9 1971 4 Sheets-Sheet l Jan. 1, 1974 H. WEHR APPARATUS FOR SECURING TOGETHER STRAPS MADE OF THERMOPLASTIC MATERIAL Filed Dec. 9 1971 4 Sheets-Sheet ,2

FIG. 2

Jan. 1, 1974 H. WEHR APPARATUS FOR SECURING TOGETHER STRAPS MADE OF THERMOPLASTIC MATERIAL 4 Sheets-Sheet 3 Filed Dec. 9 1971 Jan. 1, 1914 H. WEHR 3,783,079

APPARATUS FOR SECURING 'I(')GE'1'HER STRAPS MADE OF THERMOPLASTIC MATERIAL Filed D60. 9 1971 4 Sheets-Sheet 4 FIGA United States Patent US. Cl. 156-502 Claims ABSTRACT OF THE DISCLOSURE Apparatus for binding together thermoplastic strap portions by rotating a lever which actuates means for interposing the end of a continuous strip of wire screening between the strap portions. The end is severed from the strip when the press means, also actuated by the lever, forces the strap portions together. When severed, the screening is wedged between two electrodes in the press means and completes an electrical circuit which is activated by the lever contacting a timing device at the end of its stroke. The electrical current heats the screening which fuses the thermoplastic strap portions together.

The present invention relates to apparatus for binding together thermoplastic strap portions.

Heretofore, such apparatus has bound together thermoplastic strap portions by interposing wire screening between the straps, clamping the straps together by press die means and applying an electric voltage to the wire screening thereby heating the'screening and plasticizing or fusing the straps together. I

It is the object of the invention to improve and develop such an apparatus so that the wire screening may be inserted and the straps firmly secured together-by simply pressing down a lever.

This object is accomplished according to the invention by providing an apparatus comprising one electrode in the form of a stop plate on one side of the press die and a second electrode in the form of a shoulder at the side of an anvil face situated below the press die and at the side opposite the stop plate; and a feeding device for feeding the wire screening transverse to the length of the straps and therebetween the ends of the straps to be secured together, and against the stop plate and the shoulder respectively.

The anvil face is preferably recessed with regard to the stationary contact surface of the lower strap so that in the area which binds together the strap portions, the bound strapping will lift automatically from the anvil face due to its tension once the press die moves upward.

means of driving rollers arranged behind said sidewall,

thus rendering possible a precise feeding of the wire screening which can be taken off from a supply roll of a larger size. To this effect, a magazine capable of being swung open may be positioned adjacent the driving rollers for the purpose of receiving said supply roll.

The shoulder on the anvil forming the electrode should preferably have a cutting edge at the opening of the duct, cooperating with a knife arranged at the press die for the purpose of cutting off the piece of the continuous wire screening advanced between the strap ends. Thus the piece of wire screening necessary for securing together the strap ends will be cut off at the very moment of pressing the strap ends together, clamping the wire screen between them. The feeding device should preferably be designed in such a way that the piece of wire screening advanced by said feeding device between the strap ends will be somewhat longer than the distance between the two electrodes so that, during the cutting-off, the piece of wire screening will lie in a somewhat archedup way between the shoulder of the anvil on the one hand and the stop plate of the press die on the other hand. The descending press die, due to its contact pressure, will then flatten said wire screening piece between the strap ends and press its edges firmly against the electrodes.

For actuating the press die, there is provided in accordance with the invention a hand lever which, in one of its end positions, acts on a timing device, said timing device closing the circuit for the electrodes. Thus it is made sure that a voltage for heating up the wire screening is applied to said wire screening only after all the other working steps for securing together the strap ends are completed, and after having reached a sufficiently high contact pressure as well as having established a good contact between the electrodes and the wire screening.

For producing a sufficiently high contact pressure when shifting the hand lever, said hand lever is provided with an eccentric, said eccentric being engaged with a sliding block in a groove of the press die. In order to ensure the timely advance of the wire screening, the hand lever also actuates the driving rollers which advance the wire screening via rods and a one-way locking mechanism. The stroke of said rods can be limited by providing an adjustable stop pin and a slip clutch arranged between the actuating lever of the rods and the hand lever. This adjustable stop allows a change in the rod stroke and thus a change in the length of the wire screening advance, so that the length of the piece of wire screening can be adjusted in such a way that it is somewhat longer than the distance between the two electrodes. Due to the slip clutch, the hand lever can continue its rotation even if the feed motion for the wire screening should have come to an end before said hand lever motion.

According to the invention, the clamping device comprises a self-locking tension roll and a concave tension bed arranged within the area of the contact surface and forming part of a tensioning device. No special clamps are needed. The strap portions are inserted and tensioned by starting the tension motor, with the lower strap end being held by the tension bed, and the upper strap end by the tension roll. The tension roll is pivotably mounted on the unit in the clamping angle and clamps the strap portions firmly together, even after the tension motor is stopped.

The concave design of the tension bed provides not only a larger clamping surface for the lower strap, but also biases the upper, free strap end against the base of the press die thereby providing a gap between the two straps with the press die in the open position. This gap allows the wire screening to be inserted from the side without using any special guide means.

Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example a preferred form of the invention.

In the drawings:

FIG. 1 is a lateral view of an apparatus for tensioning and securing together thermoplastic strapping, in accordance with the invention;

FIG. 2 is a vertical sectional view taken along line II-II in FIG. 1;

FIG. 3 is a top plan view of the apparatus according to FIG. 1; and

FIG. 4 is a large-scale fragmentary view of FIG. 2.

Referring now to the drawings, wherein the showings are for the purpose of illustrating a preferred embodiment of the invention and not for the purpose of limiting same, reference character designates an apparatus for tensioning and securing together thermoplastic strapping, including a base plate 11 and an upright sidewall 12 integrally connected with said base plate. A tension bed 17 is arranged in the base plate 11 at the side of the sidewall 12 facing the observer in FIG. 1. Said tension bed 17 is pivotable on a pin 13 and height-adjustable by means of a setscrew 14. The concave roughened surface of the tension bed 17 is adapted to cooperate with the tension roll 18 pivotably mounted in a housing 31 and driven, in the direction of arrow 30, by the air motor 32 (FIG. 3) via a self-locking worm gear. The air motor 32 together with the housing 31 and the tension roll 18 are supported on the sidewall 12 and pivotable around the center 33 (FIG. 1). The center 33 is arranged in such a manner that the tension roll 18 is under the clamping angle in tension bed 17 so that the tension roll 18 when rotating in the direction of arrow 30 is pressing on the tension bed 17 and tensioning the upper strap by pulling it over the lower strap 16 which is lying on the tension bed 17.

The housing 31 is under the action of the torsion spring 34 pushed onto the center 33. The torsion spring 34 biases the tension roll 18 in the direction of the arrow 35 and presses it onto the tension bed 17. The cylinder 36 of the air motor 32 serves at the same time as a handle for moving the tension roll 18 up and down. The cylinder 36 is provided with a push button 37 and a compressed air pipe connector means 38.

A vertically slidable press die 21 is arranged in a guide 39 which guide is fixed at the sidewall 12 adjacent to the housing 31 for the tension roll. The press die 21 is provided at its upper end with a horizontal groove 40 in which a sliding block 41 is slidingly arranged. The sliding block 41 is mounted on an eccentric pin 42 of a eccentric lever 43 with the eccentric lever 43 connected in a torsionproof manner to a shaft 44. The shaft 44 is supported in the guide 39 and in the sidewall 12 and carries the hand lever 45 which is also connected to the. shaft in a torsionproof manner.

Below the press die base 23 forming the upper press area there is arranged an anvil face 25 on which the lower strap end 16 lies during the securing-together operation. The anvil face 25 is somewhat recessed compared with the other contact surface 46 of the base plate 11. At the front side of the press die base 23, a stop plate 28 is arranged and insulated from the press die base 23 by means of a layer 70 consisting of an electrically non-conducting material. The stop plate 28 forms one of the two electrodes and projects beyond the press area of the press die base 23 and also laps over the anvil face 25 when the press die 21 is in its lowest position (FIG. 4).

The anvil 25 has a shoulder 27 at the side opposite the side where the stop plate 28 is positioned, said shoulder 27 forming the other electrode to which current is supplied via a banana plug 47. The shoulder-electrode 27 is insulated from the housing and from the other electrode 28 arranged at the press die 21 by means of insulating layers 71a, 71b, 71c and 71d. Instead of the electrode 27 being insulated from the housing, what may be termed a mass connection may also be provided so that the current supplied to the electrode 28 will be returned with aproximately 6 volts operating voltage via the unit.

A knife 48 is attached at the lower end of the press die 21 on the side facing sidewall 12 which glides along a cutting face 49 attached to the sidewall 12. A fiat duct 50 opens out in said cutting face 49 passing through sidewall 12 and serves as a feeding duct for the wire screening 29. The wire screening 29 is drawn off in the form of a small strip from a supply roll 51 and advanced by driving rollers 52 and 53, said driving rollers 52 and 53 being supported on the base plate 11 below the air motor 36 and at the rear of sidewall 12. The supply roll is placed in a magazine 54 attached to the base plate 11 Which is capable of being swung open.

The press die 21 is furthermore equipped with a second cutting edge 72 perpendicular to the direction of unrolling of the two strap ends to be secured together, said knife edge 72 cutting off the upper strap end 15 from its supply roll during the securing-together operation (FIG. 1).

The upper driving roller 52 is provided with a one-way locking mechanism 55 (shown in FIG. 3), and is operated via rods 56, 57 and 58 by means of a hand lever 45. Said rods include the rocking lever 56, the connecting rod 57 and the actuating lever 58. The actuating lever 58 is pivotably mounted on the shaft 44 of the hand lever 45 and connected to the hand lever 45 via a slip clutch 59.

The rods 56, 57 and 58 reach their lower end position when the connecting rod 57 is butting against the housing of the locking mechanism 55. At the upper end position of the rods, there is provided a stop bar 61 and an adjustable stop pin 60 against which butts the upper end of the connecting rod 57.

The stop bar 61 is arranged at the upper edge of the sidewall 12. A shift finger 62 arranged at the hand lever also butts against the stop bar 61 when the hand lever 45 is in one of its two end positions. In the other end position of the hand lever 45, the shift finger 62 depresses a contact stud 63 of a timing device 64 which applies an electric voltage to the electrodes 27 and 28 and leaves the current on until the piece of wire screening 29 has been sufficiently heated in order to achieve a good fusioning together of the strap ends in the securing-together area.

OPERATION A plastic strap placed around a package denoted by letter P (shown in FIG. 1) is drawn with its lower end 16 over the base plate 11 of the unit and inserted in tension bed 17. The upper end 15 of the strapping is placed over the lower end 16 and in the tension bed 17. The tension roll 18 contacts the strap end 15 when the air motor 32 is pressed downward, whereby the torsion spring 34 presses the housing 31 downwards so that the tension roll 18 is resting firmly on the strap end 15.

By pressing the pushbutton 37, the air motor 32 is started, rotating the tension roll '18 in the direction of arrow 30, thus tensioning the strap end 15 by pulling it over the strap end 16, the strap end 16 being held by the roughened surface of tension bed 17. While rotating, the tension roll 18 is gradually drawn tighter and tighter against the tension bed with the stripping tension increasing. As soon as a sufliciently high strapping tension has been reached, the air motor 32 is stopped. The self-locking worm gear prevents the tension roll 18 from rotating in the opposite direction so that the strap ends 15 and 16 are firmly held and pressed together by said tension roll 18. During and after tensioning, the upper strap end 15 lies against the press die base 23 and is prevented from slipping forward by the stop plate 28.

The hand lever 45 is now brought from its one end position (shown in FIG. 1) into its other end position by being moved in the direction of the dot-dash arrow. At the beginning of this movement, the slip clutch 59 rotates the actuating lever 58 which then lifts the connecting rod 57, whereby the rocking lever 56 connected to said connecting rod 57 rotates the driving roller 52 in such a way that the wire screening 29 in the duct 50 is advanced toward the press area and fed between the upper strap end 15 and the lower strap end 16. This advance movement is stopped when the wire screening 29 is butting against the press area of the press die 23 (as shown in FIG. 4). When moving the hand lever 45 further in the direction of the dot-dash arrow, the connecting rod 57 butts against the stop pin 60. The actuating lever 58 is thus stopped in its movement, the slip clutch 59 slipping to permit this.

:By moving the hand lever 45, the sliding block 41 is displaced in the groove 40, and the press die 21 moved downward by the eccentric lever 43. The press die base 23 is then pressing the strap ends 15 and 16 firmly against each other, with the knife 48 cutting off the wire screening 29 at the orifice of duct 50 in cooperation with the upper edge of the shoulder 27 having a cutting edge 73.

Due to the high contact pressure, the slightly arched piece of wire screening 29, being somewhat longer than the distance between the stop plate 28 and the shoulder 27, will be flattened out and its edges 74 and 75 firmly pressed against the electrodes 27 and 28.

When the contact pressure is sufficiently high, the hand lever has reached its other end position. In this position, the shift finger 62 on the hand lever presses against the contact stud 63 of the timing device 64, whereby the electric current is switchedon and a voltage supplied to the electrodes 27 and 28 so that the wire screening 29 placed between said electrodes 27 and 28 will be heated, softening or plasticizing locally the surfaces of the strap ends 15 and 16 facing each other, so that they will be firmly connected with each other and with the wire screening.

As soon as a sufiiciently firm connection between the strap ends has been obtained, the timing device 64 cuts off the current. A short time thereafter the unit may be opened, that is, the hand lever may be moved back into its initial position and the tension roll released. By moving back the hand lever 45 into its initial position, the press die 21 is moved upward. Due to the high tension of the strapping now secured together, it will lift automatically from the anvil face 25. By moving the air motor 32 upward, the tension roll 18 will be released and lifted from the strap ends. During this operation, the wing 65 attached to the hand lever 45 may be used as a counterpressure plate for the hand when moving the air motor 32 upward. By moving back the hand lever 45 into its initial position, the rods 56, 57 and 58 will also be returned to their initial position, the actuating lever 58 slipping on the slip clutch 59 as soon as the connecting rod 57 is butting against the housing of the backrun locking mechanism 55 when the rods have reached their lower end position. Due to the one-way locking mechanism 55, the driving rollers 52 and 53 will not reverse during this operation.

Although a particular embodiment of the invention is herein disclosed for purposes of explanation, it is to be understood that I do not limit myself to the specific embodiment thereof, and it is apparent that various changes may be made, for example, in the way the press die 21 is actuated. As already mentioned, it would also be possible to provide only one electrode and to have the return current effected by what may be termed mass connection through the piece of wire screening. There might also be provided a hand-operated tensioning device instead of an air motor. It would also be possible to provide an annular magazine for the wire screening, arranged around the air motor, instead of a magazine capable of being swung open.

Having thus described my invention, I claim:

1. In an apparatus for securing together thermoplastic strap portions in overlying relationships comprising clamping means for holding said strap portions in overlying relationships; means for interposing wire screening between said strap portions; means for pressing together said strap portions in the area of said wire screenings; means for actuating said pressing means; means applying electric voltage to said wire screening; the improvement comprising:

said pressing means including cooperable press die and anvil elements positioned to maintain said strap portions therebetween;

Said electric voltage applying means including a first electrode positioned with respect to said press die and anvil elements to provide stopping means for said screemng;

said means for interposing said screening including driver roller means feeding said screening between said die and anvil elements and abutting said screening against said stopping means;

said electric voltage applying means including a second electrode positioned with respect to said die and anvil elements to provide continuous circuit means from said first electrode through said screening to said second electrode.

2. The apparatus of claim 1 further including a base element contacting a surface of one of said strap portions and adjacent said anvil element wherein said anvil element is recessed with reference to said base element.

3. The apparatus of claim 1 further including a sidewall element adjacent said anvil element wherein said means for interposing said screening further includes duct means having an outlet communicating with and spaced between the face of said die and anvil elements; said driver roller means positioned on one side of said sidewall and driving said screening through said duct means.

4. The apparatus of claim 3 wherein said duct means communicates with magazine means adapted to receive a roll of continuous metal screening; said driver roller means feeding said screening from said magazine means through said duct means and between said anvil and die elements.

5. The apparatus of claim 4 wherein said second elec trode is further positioned at said outlet and has a cutting edge in cooperating relationship with a knife, said knife adjacent to said die element and also in cooperating relationship with said die element, whereby a piece of said screening material is severed.

6. The apparatus of claim 5 wherein said driving roller means advances a section of said screening a length somewhat longer than the distance between said first and second electrodes, thereby insuring a sound connection between said first and second electrode.

7. An apparatus for securing together thermoplastic strap portions in overlying relationships comprising clamping means for holding said strap portions in overlying relationships; means for interposing wire screening between said strap portions; means for pressing together said strap portions in the area of said wire screenings; means for actuating said pressing means; means for applying electric voltage to said wire screenings including an electric current; the improvement comprising:

said actuating means including a lever having two end positions;

said means for applying electronic voltage including a timing device for closing said circuit;

said lever at one of its two end positions contacting said timing device thereby applying voltage to said screening.

8. The apparatus of claim 7 wherein said pressing means includes cooperable die and anvil elements which are positioned to maintain strap portions therebetween;

said actuating means further including said lever in cooperating relationship with an eccentric lever;

said eccentric lever contacting said die element and also engaging a sliding block;

saidsliding block positioned in a groove of said die element. 1

9. The apparatus of claim 7 wherein:

said actuating means further includes said lever in cooperating relationship with an actuating lever, a connecting rod and a rocking lever, said lever pivotably connected to said actuating lever, said actuating lever pivotably connected to said connecting rod, said connecting rod pivotably connected to said rocking lever, said rocking lever attached to said inter- 10 posing means and to a one-way locking'mechanism, said mechanism further attached to said interposing means.

10. The apparatus of claim 9 wherein:

means limiting the movement of said actuating lever and slip clutch means permitting further rotation of said lever following contact of said actuating lever with said stop means.

References Cited UNITED STATES PATENTS 3,442,733 5/1969 Vilcins 156-580 X 3,442,734 5/1969 Ericsson 156-580X US. 01; X.R.

said actuating means further includes adjustable stop 15 580 

